1. Field of the Invention
The present invention relates to a vacuum pump that is communicated with an external container to suck gas contained within the external container, and more particularly, to a vacuum pump that can suppress the propagation of vibrations to the external container without the use of dampers.
2. Description of the Related Art
A vacuum pump, such as a turbo-molecular pump or a thread groove-type pump, is known, which is communicated with an external container to suck gas contained within the external container. The vacuum pump is widely used to conduct a vacuum process in which a processing gas within a chamber is exhausted during dry etching, CVD or the like, with a semiconductor manufacturing apparatus, a liquid crystal manufacturing apparatus or the like. The vacuum pump is also used in a measuring apparatus for an electronic microscope or the like.
The vacuum pump is constructed such that an outer cylindrical portion to be communicated with the external container is fixed at one end thereof to a base so that the gas within the external container is introduced into the interior of the outer cylindrical portion at the one end thereof. In the interior of the outer cylindrical portion, a rotor portion and a stator portion are disposed, which are connected directly to or connected through other components to the base. The outer circumferential surface of one of the rotor portion and the stator portion are confronted with the inner circumferential surface of the other to define a gas transferring section for transferring the gas between the rotor portion and the stator portion.
By the rotation of the rotor portion, the gas within the gas transferring section is transferred, and the gas within the external container is sucked therein.
In case of a turbo-molecular pump, a plurality of spacers are disposed on the stator portion coaxially to the rotor portion, and stator blades are respectively disposed between the adjacent spacers to project toward the rotor portion. Rotor blades are disposed on the rotor portion to respectively project into spacers between the adjacent stator blades. The rotor blades, when rotated, collide against and thus transport the gas molecular.
In case of a thread groove-type pump, a thread groove is formed on one of the confronted circumferential surfaces of the rotor portion and the stator portion. Thus, when the rotor is rotated, the gas is transferred using the gas viscosity.
The vacuum pump described above is applied, for instance, to an electronic microscope or other apparatuses, that are largely affected by minute vibrations.
In a related art, the vacuum pump is formed of material which can easily propagates vibrations therethrough, that is, the rotor portion and the base are formed of aluminum alloy (the logarithmic attenuation ratio thereof with respect to vibrations is about 0.0002), and the outer cylindrical portion and bolts for connecting components together are formed of SUS alloy (the logarithmic attenuation ratio thereof with respect to vibrations is about 0.01). Consequently, the vibrations associated with the rotation of the rotor portion are propagated through the stator portion and the outer cylindrical portion to adversely affect the external apparatus connected thereto.
For this reason, as shown in FIG. 4, a technical solution has been proposed, in which a damper D is interposed between a pipe C of the external container and the outer cylindrical portion 116 of the vacuum pump 100 to prevent vibration caused due to the rotation of the rotor portion or the like from being propagated to the external container connected to the vacuum pump.
As an example of the damper D, a thin, SUS-made cylindrical member whose circumferential surface is bent into a bellows shape, and which is coated with a silicon rubber or the like is used. This damper D is designed such that the natural frequency of the entire damper D system is 20 Hz or less in order to have the excellent damping property. During the use of the vacuum pump 100, the damper D is tightened with a hose band or the like externally mounted to the damper D.
However, the use of the damper D as a solution of avoiding the propagation of the vibrations of the vacuum pump 100 requires an extra space in the axial direction corresponding to the length of the damper D. The space required for mounting the damper D to the vacuum pump 100 is generally about 10 cm in the axial direction. The increased cost corresponding to the damper D is also required.
The mounting and removable of the damper D requires labor and is troublesome. The property of the damper D may be changed depending on the mounting state of the damper D.
Additionally, the bellows-shaped member described above can not be formed of a high-rigidity member or a thick member because the bellows-shaped member is required to exhibit an excellent vibration suppressing effect. For this reason, if the excessive force due to the rotational torque of the rotor portion acts on the member, the member may be broken. It is conceivable to arrange a reinforcing member such as a rotation preventive member in order to eliminate the breakage, but the arrangement of the reinforcing member requires an extra cost and makes the structure of the apparatus complicated. Consequently, the maintenance work such as the mounting and removal becomes troublesome.
Further, the natural frequency of the entire pump is about 10 Hz, which is close to the natural frequency of the precession of the rotor (several Hz) generated in the case where the rotor portion of the vacuum pump is supported by magnetic bearings. Consequently, the rotational shift of the rotor portion is likely to be increased due to an external force such as an earthquake, and in some cases, the protection function is activated to stop the rotor portion.
As described above, the related vacuum pump requires the damper to be mounted to the connecting portion to the external container in order to prevent the propagation of the vibrations to the external container, but the mounting of the damper increases the cost and labor and requires the extra space, resulting in the lowering of handling ability.
Further, the related vacuum pump as described above has a built-in motor, and further a certain type of the vacuum pump uses magnetic bearings as bearings. For this reason, magnetic fluxes caused by magnets of the motor and magnetic bearings may leak externally to adversely affect the connected external container such as a vacuum apparatus.
Furthermore, the related vacuum pump as described above is designed such that the outer cylindrical member to be fixed to the vacuum apparatus is electrically connected to cores of electromagnets of the motor and magnetic bearings. In the case where a switching amplifier is used as a driving amplifier for the electromagnets of each of the motor and magnetic bearings, if the voltage applied to the coil of the electromagnet by the switching amplifier is varied, the current excited in the core of the electromagnet may be transmitted through the outer cylindrical member to the external vacuum apparatus, causing an electric noise to adversely affect the vacuum apparatus.
As described above, the related vacuum pump suffers from the generated vibrations, leakage of magnetic flux, and electric noise, which lowers performance, reliability and service life of the vacuum apparatus connected to the vacuum pump.
As a technical solution for eliminating the leakage of magnetic flux to the apparatus connected to the vacuum pump, a technique is known in which the exterior of the outer cylindrical member is housed by a shielding member formed of high permeability material, such as a silicon steel plate, for shielding the magnets of the motor and magnetic bearing. However, this technical solution has a problem in that the vacuum pump is made large in size due to the provision of the shielding member in order to obtain the sufficient shielding effect. It is conceivable to arrange a shielding member just around the exterior of the motor or magnetic bearing. However, because the density of the leaking magnetic flux in this location is high, the thick shielding member is required to provide the sufficient shielding effect, resulting in the increased size and cost of the vacuum pump.
The present invention has been made in order to solve the problems mentioned above. Accordingly, a first object of the present invention is to provide a vacuum pump which can suppress the propagation of vibrations to an external container connected to the vacuum pump without the use of damper.
In addition to the first object, a second object of the present invention is to provide a vacuum pump which can avoid the external leakage of magnetic flux while suppressing the size increase and cost increase.
In addition to the first object, a third object of the present invention is to provide a vacuum pump which can suppress the transmittance of an electric noise to an external container connected thereto.
To attain the first object, the present invention provides a vacuum pump (a first arrangement) comprising: an outer cylindrical portion to be connected to an external container, the outer cylindrical portion having one end portion provided with an inlet port through which a gas within the external container is sucked; a rotor portion rotatably accommodated within the outer cylindrical portion; a stator portion disposed within the outer cylindrical portion, the stator portion and the rotor portion cooperatively defining a transferring portion for transferring the gas sucked through the inlet port; a magnetic bearing for floatingly supporting the rotor portion; a motor portion for rotatingly driving the rotor portion; a base supporting the outer cylindrical portion and the stator portion at the other end portion of the outer cylindrical member; and a vibration absorbing member, interposed between at least one of the outer cylindrical portion and the stator portion and the base, for displaceably supporting the at least one of the outer cylindrical portion and the stator portion with respect to the base, characterized in that the vibration absorbing member has a natural frequency F meeting the following formula:
F=(f1+f3)/2xc2x1(f1xe2x88x92f3)/4
where f1, f2 and f3 respectively denote a natural frequency of nutation in conical mode, a natural frequency in parallel mode and a natural frequency of procession in the conical mode, when the rotor portion is rotated at a rated speed.
In a vacuum pimp comprising: an outer cylindrical portion to be connected to an external container, the outer cylindrical portion having one end portion provided with an inlet port through which a gas within the external container is sucked; a rotor portion accommodated within the outer cylindrical portion; a stator portion disposed within the outer cylindrical portion to define a gas transferring portion in cooperation with the rotor portion; a magnetic bearing for supporting the rotor portion with respect to the stator portion in thrust and radial directions; a motor portion rotating the rotor portion with respect to the stator portion; and a base supporting the outer cylindrical portion and the stator portion at the other end portion of the outer cylindrical portion, vibrations caused on the motor portion and the magnetic bearing are propagated through the stator portion to the base, and further propagated from the base through the outer cylindrical portion to the external container.
Therefore, if the vibration absorbing member is interposed between the stator portion and the base so that the stator portion is displaceably supported to the base, the vibrations caused on the motor portion and the magnetic bearing are propagated from the stator portion to the base after the vibrations are absorbed and attenuated by the vibration absorbing member. Accordingly, it is possible to suppress the propagation of the vibrations to the external container. Further, if the vibration absorbing member is interposed between the outer cylindrical portion and the base so that the outer cylindrical portion is displaceably supported to the base, the vibrations caused on the motor portion and the magnetic bearing are propagated from the base to the outer cylindrical portion after the vibrations are absorbed and attenuated by the vibration absorbing member. Consequently, it is possible to suppress the propagation of the vibrations to the external container.
In the present invention, by using the vibration absorbing member having the natural frequency F meeting the above-noted relationship with respect to the natural frequencies f1, f2 and f3 of the magnetic bearing, the natural frequency of the vibration absorbing member can be set not to close to the natural frequencies of the vacuum pump and the magnetic bearing. Accordingly, the rotational shift of the rotor portion is difficult to be increased due to the external force such as an earthquake, and the rotor portion can be supported stably with respect to the stator portion.
It is sufficient that the vibration absorbing member is partially disposed between at least one of the outer cylindrical portion and the stator portion, and the base. For example, the vibration absorbing member is located at a central portion of each of the segments obtained by dividing a clearance between the outer cylindrical portion or the stator portion, and the base at equal angular intervals with respect to the axis.
The vacuum pump of the first arrangement can be constructed as a vacuum pump in which the vibration absorbing member includes a silicon gel (a second arrangement).
The silicon gel can reduce the rate of the vibration propagation, especially from the low frequency, one or more orders, and thus it is possible to remarkably suppress the propagation of the vibrations.
Each of the vacuum pumps of the first and second arrangements can be constructed as a vacuum pump, in which the vibration absorbing member is interposed between the stator portion and the base, and displacement restricting means is provided for restricting a range where the stator portion is displaceable with respect to the base (a third arrangement).
In the vacuum pump arranged such that the vibration absorbing member is interposed between the stator portion and the base, the stator portion is displaceably supported with respect to the base. For this reason, the stator is displaced with respect to the base when the external force such as the earthquake occurs. The clearance between the stator portion and the rotor portion is set to be as small as possible for the purpose of transferring the sucked gas without escaping toward the inlet port side. For this reason, if the stator portion is displaced with respect to the base due to the external force, then the stator portion may be contacted with the rotor portion to damage components such as rotor blades.
Therefore, it is preferable to provide the vacuum pump with the displacement restricting means for restricting the range where the stator is displaceable with respect to the base, thereby restricting the displaceable range of the stator when the external force occurs and avoiding the contact between the stator portion and the rotor portion.
In the third arrangement, the vacuum pump can be constructed such that: the stator portion includes a protruded portion protruded substantially parallel to a plane defined by the base; a plurality of restricting holes are arranged circumferetially in the protruded portion; the displacement restricting means includes restricting bolts and restricting members, the restricting bolts being formed of a material higher in rigidity than that of the vibration absorbing member, each of the restricting bolts being loosely inserted into the respective restricting holes with a leading end thereof fixed to the stator portion; and each of the restricting member has a restricting cylinder that is fixed around a shaft of each of the restricting bolts, and that is spaced from an circumferetial surface of each of the restricting holes of the protruded portion, and two disk portions that are extended outwardly from respective end portions of the restricting cylinder and that are disposed opposite from each other with respect to the protruded portion while being spaced from the protruded portion (a fourth arrangement).
To attain the first object, the present invention provides a vacuum pump (a fifth arrangement) comprising: a flange portion to be connected to an external container, the flange portion having an inlet port through which a gas within the external container is sucked; an outer cylindrical portion having one end side connected to or integral with the flange portion; a base connected to the other end side of the outer cylindrical portion, the base, the flange portion and the outer cylindrical portion cooperatively defining a hollow portion communicating with an interior of the external container through the inlet port; a stator portion supported to the base, and accommodated within the hollow portion; a rotor portion accommodated within the hollow portion; a bearing rotatably supporting the rotor portion with respect to the stator portion; a motor portion for rotatingly driving the rotor portion, supported by the bearing, with respect to the stator portion; and vibration absorbing means, including a material having a vibration absorbing property, for reducing propagation of vibration using elastic and/or viscous property, the vibration absorbing means being disposed at at least one of the flange portion, the outer cylindrical portion, the base, the stator portion, and joint portions respectively connecting two members selected from the flange portion, the outer cylindrical portion, the base, and the stator portion.
In the vacuum pump of the fifth arrangement, the vibration absorbing means, including a material having a vibration absorbing property, for reducing propagation of vibration using elastic and/or viscous property, is disposed at at least one of the flange portion, the outer cylindrical portion, the base, the stator portion, and joint portions respectively connecting two members selected from the flange portion, the outer cylindrical portion, the base, and the stator portion.
For this reason, the vibrations caused on the motor and the bearing in the interior of the vacuum pump when the rotor portion is rotated are surely reduced by the vibration absorbing means, and unlikely to be propagated to the flange portion. The vibrations caused on the motor and the bearing are propagated to the external container after being reduced by the vibration absorbing means. Accordingly, it is possible to reduce the propagation of the vibrations to the external container without using a solution in a related art in which a vibration absorbing member, such as a damper, is arranged between the flange portion and the external container.
The vibration absorbing means may be disposed at the flange portion, the outer cylindrical portion, the base and/or the stator portion, and/or may be disposed at the joint portion between the flange portion and the outer cylindrical portion, the joint portion between the outer cylindrical portion and the base, and/or the joint portion between the stator portion and the base. In the case where the vibration absorbing means is disposed at the flange portion, the outer cylindrical portion, the base and/or the stator portion, these members may be partially or entirely formed of a material having the vibration absorbing property, or the material having the vibration absorbing property or a member having the vibration absorbing property may be added to an available flange portion, outer cylindrical portion, base and/or stator portion. In the case where the vibration absorbing means is disposed at the joint portion between the flange portion and the outer cylindrical portion, the joint portion between the outer cylindrical portion and the base, and/or the joint portion between the stator portion and the base, a joint member(s) may be interposed between the flange portion and the outer cylindrical portion, between the outer cylindrical portion and the base, and/or between the stator portion and the base, and the joint member may be partially or entirely formed of the material having the vibration absorbing property, or the material having the vibration absorbing property or the member having the vibration absorbing property may be added to the joint member. The flange portion, the outer cylindrical portion and the vibration absorbing material therebetween may be formed integrally, the outer cylindrical portion, the base and the vibration absorbing material therebetween may be formed integrally, and the stator portion, the base, and the vibration absorbing material therebetween may be formed integrally.
The external container may be a chamber or the like of a semiconductor manufacturing apparatus or a electronic microscope, in which a vacuum is maintained, or may be a pipe connected to a container such as the chamber. The flange portion may have the inlet portion connected to the container such as the chamber to suck the gas directly from the container, or may have the inlet portion connected to the pipe connected to the chamber or the like to suck the gas from the pipe.
The vacuum pump of the fifth arrangement can be constructed such that: the outer cylindrical portion has an outlet port through which the gas within the hollow portion is discharged; and the vibration absorbing means is disposed at at least one of the flange portion, the outer cylindrical portion and the joint portion connecting the outer cylindrical portion and the flange portion (a sixth arrangement).
Each of the vacuum pumps of the fifth and sixth arrangements can be constructed such that: the base has an outlet port through which the gas within the hollow portion is discharged; and the vibration absorbing means is disposed at at least one of the flange portion, the outer cylindrical portion, the base, and joint portions respectively connecting two members selected from the flange portion, the outer cylindrical portion, and the base (a seventh arrangement).
Each of the vacuum pumps of the fifth to seventh arrangements can be constructed such that the vibration absorbing means includes at least one of a spring member, a rubber member formed of a rubber, a gel member formed of a gel material and a bellows (an eighth arrangement).
Each of the vacuum pumps of the sixth to eighth arrangements can be constructed such that: the flange portion is discrete from the outer cylindrical portion; and the vibration absorbing means is disposed at the joint portion connecting the flange portion and the outer cylindrical portion (a ninth arrangement).
In the vacuum pump of the ninth arrangement, the vibrations propagated to the outer cylindrical portion, including the vibrations of the motor and the bearing caused within the vacuum pump when the rotor portion is rotated and the vibrations due to an external factor such as a vibration propagated from a back pump, are all reduced by the vibration absorbing means, and then propagated to the external container. Accordingly, it is possible to remarkably reduce the vibrations on the external container.
The vacuum pump of the ninth arrangement can be constructed as a vacuum pump comprising: an outer cylindrical portion defining a hollow portion accommodating therein a stator portion and a rotor portion rotatable with respect to the stator portion; a cylindrical flange portion discrete from the outer cylindrical portion and having an inlet port for a gas contained within an external container; elastic supporting means, fixed to the outer cylindrical portion, for elastically displaceably supporting the flange portion with respect to the outer cylindrical portion; a communicating member communicating the inlet port of the flange portion with the hollow portion of the outer cylindrical portion; and a motor for rotating the rotor portion with respect to the stator portion to suck the gas contained within the external container from the inlet port of the flange portion through the communicating member to the hollow portion of the outer cylindrical portion. That is, the vacuum pump is provided with the elastic supporting means serving as the vibration absorbing means for reducing the propagation of the vibration from the outer cylindrical portion to the external container. Accordingly, the required space in the axial direction is not increased in comparison to a solution in a related art in which vibration absorbing means such as a damper is disposed between the flange integral with the outer cylindrical portion and the external container. By arranging the elastic supporting means on the outer circumferential surface of the outer cylindrical portion, the space in the axial direction can further be made small.
In the vacuum pump of the ninth arrangement, the vibration absorbing means can also be used as the communicating member communicating the inlet port of the flange portion with the hollow portion of the outer cylindrical portion. In this case, if the vibration absorbing means is directly fixed to the circumferential surface of the outer cylindrical portion, a hermetical sealing state must be established between the outer cylindrical portion and the elastic supporting means. If the vibration absorbing means is fixed with respect to the outer cylindrical portion through an additional member, the hermetical sealing state must be established between the additional member and the outer cylindrical portion and between the additional member and the vibration absorbing means.
In the vacuum pump of the ninth arrangement, the vibration absorbing means may include an elastic member connecting the outer circumference of the outer cylindrical portion to the flange portion, and a bellows juxtaposed to the elastic member to connect the outer circumference of the outer cylindrical portion to the flange portion. In this vacuum pump, if the vacuum pump is activated to reduce the internal pressure in the outer cylindrical portion, the bellows contracts in the axial direction. The bellows also contracts together with the elastic member depending on the displacement of the flange portion with respect to the outer cylindrical portion due to the vibrations and the like. This makes it possible to define a gas passage that extends from the flange portion to the outer cylindrical portion and that is hermetically sealed from the exterior, thereby eliminating the mixture of other members and exterior gas outside the bellows into the vacuum pump. In this case, it is preferable to dispose the elastic member outside the bellows, because molecular contained in the elastic member can be surely prevented from mixing and entering into the vacuum pump by the bellows. It is preferable that a spring constant of the bellows in the axial direction is smaller than that of the elastic member in the axial direction. This makes it possible to prevent the breakage of the bellows even in the case where the pressure within the outer cylindrical portion is increased or decreased or an external impact is applied.
The vacuum pump of the ninth arrangement can have restricting means for restricting a position of the flange portion to a predetermined range with respect to the outer cylindrical portion (a tenth arrangement).
In the vacuum pump of the tenth arrangement, the restricting means restricts the position of the flange portion to the predetermined range with respect to the outer cylindrical portion. Accordingly, even if the large impact such as the breakage of the rotor portion occurs, the elastic member and the bellows are protected from being broken, which, in turn, lowers a possibility of an accident in which the vacuum pump is removed from the external container or the pipe connected to the external container. Thus, the high safety can be ensured.
The present invention achieves the second object by providing the vacuum pump of each of the fifth to tenth arrangements, which further comprises a sheet-like magnetic shielding material that is disposed radially outwardly at the stator portion and the rotor portion to circumscribe the stator portion and the rotor portion, and that is disposed along an inner circumferential surface of the outer cylindrical portion (an eleventh arrangement).
In the vacuum pump of the eleventh arrangement, the magnetic shielding material is disposed outwardly of the stator portion and the rotor portion to avoid the external leakage of the magnetic fluxes caused by electromagnets, permanent magnets and the like. constructing the motor and the magnetic bearing. This magnetic shielding material is disposed outwardly of the stator portion and the rotor portion and separated predetermined distances from the electromagnets and permanent magnets that generate the magnetic fluxes. Accordingly, the magnetic shielding material can effectively eliminate the leakage of the magnetic fluxes with a reduced thickness thereof, and thus the cost of the magnetic shielding material and the installation space therefor can be suppressed. Since the magnetic shielding material is disposed inwardly of the outer cylindrical portion, it is protected by the outer cylindrical portion and less likely to be damaged.
The present invention achieves the third object by providing the vacuum pump of each of the fifth to eleventh arrangements, which further comprises: an insulative portion formed of an electrically high-insulative resistance material, which is disposed at the joint portion connecting the outer cylindrical portion and the flange portion (a twelfth arrangement)